Understanding the glycemic index

Definition

The glycemic index (GI) is an indicator that measures the ability of a carbohydrate-containing food to raise blood sugar levels after consumption.

It is expressed on a scale from 0 to 100, by comparing the glycemic response of a food to that of pure glucose (GI = 100).

In concrete terms, the higher the glycemic index, the faster the rise in blood sugar.

Why it's important

After a meal containing carbohydrates, blood sugar levels rise, triggering the release of insulin, a hormone that regulates blood sugar levels.

The speed and intensity of this increase vary according to the foods consumed. This is where the glycemic index comes in.

A high-GI food generally causes a rapid rise in blood sugar levels, followed by a more or less marked drop. Conversely, a lower GI food causes a more gradual rise.

This can influence :

• the feeling of satiety
• energy levels
• appetite management

However, it is important to understand that the glycemic index should not be interpreted in isolation.

How the glycemic index works

The glycemic index depends primarily on the speed at which carbohydrates are digested and absorbed.

The faster a food is converted into glucose, the higher its GI. Conversely, if digestion is slowed down, the glycemic response will be more moderate.

Foods are generally classified as follows

• Low GI: less than 55
• Moderate GI: between 55 and 70
• High GI: over 70

This classification remains indicative and should be used with caution.

What science says

The glycemic index has been used in nutrition for several decades, particularly in the management of diabetes.

Research shows that a diet based on lower GI foods can, in certain contexts, contribute to :

• better glycemic control
• a more stable feeling of satiety

However, results are highly dependent on overall diet and lifestyle.

Important points :

• gI alone is not enough to judge food quality
• the combination of foods in a meal modifies the glycemic response
• response varies from one individual to another

Sources: Harvard School of Public Health, NIH, American Journal of Clinical Nutrition.

The limits of the glycemic index

The glycemic index is a useful but imperfect tool.

It is measured on foods eaten alone, which does not always reflect the reality of a complete meal. Adding protein, fat or fiber can slow carbohydrate absorption and alter glycemic response.

Nor does the GI take into account the quantity consumed. This is why we also talk about glycemic load, which takes into account both the quality and quantity of carbohydrates.

Finally, some high-GI foods can be of good nutritional value (such as certain fruits), while some ultra-processed products can have a moderate GI but low nutritional quality.

Examples of foods

To help you find your way around, here are a few examples.

Low GI :

• legumes
• oat flakes
• sweet potato
• most vegetables

Higher GI :

• white bread
• white rice
• potatoes (depending on cooking)
• sweet products

These values may vary according to cooking, processing and combination with other foods.

Factors influencing the glycemic index

The glycemic index of a food is not fixed. It can vary according to a number of factors.

Cooking plays an important role: the more a food is cooked, the faster its carbohydrates can be assimilated. Industrial processing (refining) often increases the GI.

The presence of fiber, fat or protein in a meal generally slows carbohydrate absorption.

In practice :

• a single food is not equivalent to a complete meal
• food combinations are essential

Food order and glycemia

The glycemic index of a meal depends not only on the foods eaten, but also on the order in which they are eaten.

Studies have shown that eating foods in a certain order can modify glycemic response.

When carbohydrates are eaten first, especially if they are low in fiber, blood sugar levels rise more rapidly. This leads to a greater insulin response, followed by a sharper drop.

Conversely, eating fiber (vegetables) first, followed by protein and fat, before carbohydrates, slows down digestion and absorption of glucose.

In concrete terms, the recommended order is :

1. vegetables (fiber)
2. proteins and lipids
3. carbohydrates

Result:

• a more gradual rise in blood sugar levels
• more stable energy after the meal
• more moderate insulin response

This principle doesn't require changing the food, just the order in which it is eaten.

Practical advice

The aim is not to eliminate all high-GI foods, but to understand how to integrate them intelligently.

In practice:

• combine carbohydrates with fibers, proteins or lipids
• give preference to minimally processed foods
• vary carbohydrate sources
• avoid isolated fast sugars (especially outside mealtimes)

Adopting a global approach helps achieve a more stable glycemic response, without excessive rigidity.

To remember

The glycemic index provides a better understanding of the impact of carbohydrates on blood sugar levels, but it must always be interpreted in a global context.

Keep in mind:

• High GI does not mean bad
• Low GI does not mean perfect
• meal composition is essential
• the answer is individual
• overall balance remains the priority